The elbow region is the most common site at which the ulnar nerve is prone to a localized neuropathy. Diagnosis of ulnar nerve entrapment at elbow is made on the basis of history, lacal neurologic finding, nerve conduction studies and electromyography. Electrophysiologic test is simple, relatively quick, and accurate method for the diagnosis of peripheral nerve lesion. Therefore, electrodisgnosis makes it possible to identify and localize the early stage of entrapment lesion. Definitive diagnosis of ulnar nerve entrapment at elbow requires electromyographic demonstration of decreased ulnar nerve conduction velocity across the elbow and depressed sensory nerve action potentials. The purpose of this study were to analyze the electrophysiologic findings of patients with an established ulnar nerve entrapment at elbow compared to normal eonduction velocity of our laboratory. And we evaluate the correlation of clinical symptom with the electromyographic findings. Twenty five subjects were studied, 22 men and 3 women, aged from 5 to 62 years. The results were as follows . 1. The mean motor conduction velocity of ulnar nerve across elbow were 32.85±10.21 m/sec. The longer duration of symptom were, the slower conduction veloctity across elbow were. 2. Among the 25 patients, motor conduction velocity of ulnar nerve at forearm segment decreased in 15 patients(60%). As the motor conduction velocity of the ulnar nerve across elbow became slower, thst of forearm segment were slower. 3. In 19 patients (76%) among the 25 patients, sensory evoked potentials revealed prolonged distal latency or were not evoked. 4. On needle electrodiagnostic study, positive sharp wave or fibrillation potentials could be found in abductor digiti minimi first dorsal interosseus and/or flexor carpi ulnaris muscles in 22 patients(88%).